Maybe because it's a Russian program? It's kind of a "no shit" statement but there's an definite attraction towards using a software written by someone from your own country, especially if you aren't too fluent in English.
There is good games made with qsp just as there good games made in whatever else, the same applies to bad as well.
Seeing renpy games with horrible machine translated English, I'm quite sure Russians love that and other engines as well.